To date, an information processing device that uses a storage device including a nonvolatile semiconductor as storage is known. As an example of such an information processing device, an information processing device that uses a solid state drive (SSD) having NAND type flash memory as storage is known.
In NAND type flash memory, writing and reading is performed in units of pages each of which contains a plurality of memory cells for retaining data, and erasure of data is performed in units of blocks each of which contains a plurality of pages. The memory cell, however, is degraded each time data is rewritten, and therefore becomes incapable of normally recording information when rewriting of data is performed many times. For this reason, if data is frequently rewritten to the same memory cell, the memory cell becomes incapable of normally recoding information. As a result, a block containing the memory cell that has become incapable of normally recording information becomes a defective block.
To address this, a technique of wear leveling is known. In wear leveling, the numbers of times data is written to memory cells and the numbers of times data is erased are made uniform, so that occurrence of a defective block is inhibited and the lifetime of an SSD is improved. For example, an SSD to which the technique of wear leveling is applied causes the numbers of updates of the entire memory cells included in the SSD to be uniform by moving data stored in a block where updating is performed frequently to a block where the number of updates is small.
A related technique is disclosed in, for example, Japanese Laid-open Patent Publication No. 2007-323224.
The technique of wear leveling mentioned above, however, does not thoroughly solve restrictions on the number of times data is written and the number of times data is erased in one SSD, but only prolongs the lifetime of the SSD. For this reason, it is impossible for an information processing device to continue to use one SSD without consideration of the number of times data is written and the number of times data is erased in a flash memory.